Currently there is a strong need for improved drag reduction and consequent fuel conservation on all ocean going vessels. Numerous antifouling coatings have been developed and several in-water hull cleaning techniques are in use or are being developed. Most of the antifouling coatings depend on a leaching action to prevent attachment of marine fouling organisms on the hull. After a time, however, the marine organisms will grow to cover portions of the wetted hull and a hull scrubbing will be needed to remove them.
Just how effectively the rejuvenated or cleaned coating resists further organisms is not clear. An ineffective coating or an untreated hull quickly becomes fouled and consequently drag and fuel consumption are increased. However, a scrubbed hull that still has enough coating to resist marine organisms is capable of providing additional months of fuel efficient, low-drag operation. Since the dry dock time, costs for recoating a hull, and in-water hull cleaning schedules are important considerations for ocean-going vessels, it is necessary to determine the maximum time a hull coating effectively resists marine organisms under various operational and cleaning conditions.
Existing laboratory techniques for the leach rate measurement call for placing an antifouling coated panel in a beaker of seawater of known volume and stirring or agitating it. At selected times small samples are removed from the solution and analyzed for copper content, by using, for example, an atomic absorption spectrophotometer. The results are used to determine the leach rate of the antifouling coating for the purposes of assessing its effectiveness and functional life. Obviously such a technique is inadequate and is not adapted for use on in-water ship hulls that pass through waters having different salinities, temperatures, etc., and have varying operational histories all of which effect leaching rate and the accumulation of marine organisms differently. In short, the laboratory methods produce results that cannot be extropolated to in-situ hull measurements or conditions.
Thus, there is a continuing need in the state-of-the-art for a method and apparatus for determining the in-situ leach rate of hull coatings which can assist in the optimization of antifouling coating design and hull cleaning procedures and in turn can lead to significant drag reduction and increased fuel conservation.